A variety of file-sharing programss is available on several different networks. Availability depends partly on operating system, and different networks have different features (for example, multiple-source downloads, different sorts of search limiting, and so on). Several major file-sharing programs contain spyware, which many users wish to avoid.

In the early days, client software was protocol-specific, so you had "Napster" clients, and you had "Gnutella" clients. There is an everpresent push towards making the GUI-side of things capable of using multiple protocols. After all, why should a user have to load up several different applications to do what is, in their mind, the same thing?

In cases where there is perceived value in collecting, some people will have lots to share and will find themselves surrounded by eager people. This can cause problems when the collector cannot keep up with demand. Decentralization is one means to alleviate this problem, especially in cases where it is possible to ensure that multiple copies of a popular item are available from multiple sources (even simultaneously, as with multi-source downloading).

Concepts like hoarding come about where the one centralized person will collect and will not later freely give away what was given. Barter and ratio systems evolve in order to reduce the impact of hoarding. Under these systems, a person will only share when they can expect to get something in return.

Napster, a centralized service, was the first major file-sharing tool and popularized file sharing for the masses. Napster was an MP3-only sharing system and was successfully shut down by legal attacks from the music industry. It was openly attacked by some artists (notably Dr. Dre, Metallica) and supported by others (Limp Bizkit, Courtney Love, Dave Mathews). Napster was a localized index for MP3 files shared by the users logged into the system. It included IRC-like chat & IM features. Almost all new, major clients now follow its example in design.

Afterwards, Gnutella, a decentralized network, appeared. This service was fully open-source and allowed users to search for almost any file type; users could find more than just MP3s on these networks. It was created/supported in response to threats towards centralized bodies like Napster. The thought behind decentralization is that no one broken link can bring about the downfall of all members. But Gnutella has experienced growing pains since its use skyrocketed.

Napster and Gnutella continue to define file sharing today, forming the extreme at both ends. Gnutella, a free and open protocol and service, with it's lawless structure but poor scalability. Napster with it's high speed but inability to convince the music industry of its relevance despite millions of dollars in investment.

Most file-sharing systems since have sought to ride the line between these two extremes.

There has been a great discussion over perceived and actual legal issues surrounding file sharing. In circumstances where trading partners are in different countries with different legal codes, there are significant problems to contend with. What if a person in Canada wishes to share a piece of source code which, if compiled, has encryption capabilities? In some countries, a citizen may not request or receive such information without special permission.

Through 2001 and 2002, the entire file-sharing community has been in a state of flux, since record companies and RIAA try to shut down as much of this as possible. Even though they have forced Napster into cooperating against copyright violations, they are way behind, since the community has flourished and produced lots of different clients, though not as many different underlying protocols. The second generation of P2P protocols, such as Freenet are not as dependent as Napster is on a central server, making it much harder to shut down these systems through court actions. Another attempt (used by the maintainers of KaZaA) is to change the company's organization so that it is impossible or useless to attack it legally.

Decentralization has been widely pushed over the fear of having a centralized network attacked, either by legal disputes or hostile users. One argues that a decentralized network has no body to attack, only individual ethereal members. While the foundation protocol of the Internet TCP/IP was designed to be robust and withstand concerted attack, file-sharing and peer-to-peer systems are proving even stronger.

So today we are left with a slew of clients with functionality designed around making sharing files more effective, both in the real sense of uploading and downloading (like anti-hoarding functions) and in the more ethereal sense of being bulletproof towards legal issues (as with anonymity and decentralization).

decentralization - Implications of the end-to-end principle - A mailing list exclusively devoted to the architecture of P2P-systems, with a lot of traffic and interesting ideas passed around. Founded by Lucas Gonze, with lots of high-profile subscribers from the P2P field. Open since July 2000, and still running past Nov 2002.

The GDF - The Gnutella Developer Forum is a group for discussing extensions of the Gnutellaprotocol. It is the largest standards body for the Gnutella network, and anyone working on a servant should be a member.

A Method of Free Speech on the Internet: Random Pads (by David A. Madore) - Discusses how information can be completely separated from its creators by XORing it with chunks of random data. The resulting "pads" can then be distributed across so-called "pad archives". A pad archive neither knows what it is hosting nor does it host provably controversial data, since the data cannot be distinguished from noise. It's mainly a legal question: If the courts would outlaw hosting random data, it wouldn't work. Other than that, it's pretty safe -- interesting read, and there are already quite a lot of pad archives (thanks to Slashdot).

SafeX - Secure and Anonymous File EXchange. Just a draft with many interesting ideas to use in other projects.

OceanStore - OceanStore is "designed to span the globe and provide continuous access to persistent information". "Data is protected through redundancy and cryptographic techniques. To improve performance, data is allowed to be cached anywhere, anytime. Additionally, monitoring of usage patterns allows adaptation to regional outages and denial of service attacks; monitoring also enhances performance through pro-active movement of data. A prototype implementation is currently under development."

Who's on First Proposal - This page introduces the Who's On First (WOF) anonymous network, which is the working title of a proposal for a more flexible and reliable anonymous communication network than that provided by current Type I and II remailers.

JetFile - Proposal for a scalable distributed file system (some parts are centralized).

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